The Gaussian-School of Higher-Arithmetic (1831, updated 2022); tutorial #21 page 3.

The Arithmetic of Clocks, page 3.

The green zero-circle is a member of a doubly unbounded (from minus infinity to plus infinity) geometric series of circles and we can arbitrarily assign any member of the infinite set to be the zero-circle; the index numbers of all the others just fall into line with our arbitrary selection from within the double ended infinite geometrical progression of numerical magnitude.